Since a method of producing aluminium from alunite is only in the formative stage. bauxite is the ore chiefly sought throughout the world in the present crisis. Podlike in form it is found in grea? quantities in Arkansas and to lesser ex-fent in Georgia. Tennessee, Massachusetts and Virginia. But the largest supply is imported from Surinam, Dutch Guiana in South America.
At these localities open an underground mining are employed to extract the lumpy and fine-grained mineral which is loaded onto mine cars for transportation to the mill for crushing and washing to r"move.clay with its silica impurity. The bauxite is then poured into drying kilns to drive off moisture and is ready for shipment to refineries for further processing.
In the commonly-used Bayer refining method the washed. crushed and dried bauxite is ground into powder. mixed with a hot solution of sodium hydroxide or caustic soda and pumped into large pressure tanks or digesters. Here the caustic soda dissolves the aluminium hydroxide leaving a sodium aluminate solution. Filtering and precipitating this solution in tanks as high as a five storey building gives fine crystals of alum minium hydroxide which become alumina upon further heating.
To change the powdery alumina into metal aluminium enormous quantities of electricity are required so the material is shipped to places where power is plentiful such as Niagara Fall. N. Y. and to the Southeast where the TVA is located. Recently new plants have been constructed in the Pacific Northwest to take advan-being constructed near Grand Coulee Dam. tage of the electricity from giant generators Finat reduction of alumina to metallic alummium-involves the dissolving of the former in a bath of cryolite which separates it into its component parts of oxygen which passes off and metallic aluminium which remains The metallic aluminium is tapped into mixing ladles and cast into individual "pigs" which are further purified by remelting and then cast into ingots for use in industry.
Qualities of aluminium which make it especially valuable for use in defence are lightness. high reflectivity for heat and light. strong resistance to corrosion. high thermal and ekctrical conductivities and good workability.
No other metal can be obtained in so many different forms and its products include those fabricated by "very metal-working process. It is rolled into sheets ten times as thin a3 newspaper. I+ is stranded into cable for transmission lines. rolled into structural shap*s and extruded. like squeezing toothpaste, into airplane parts. Even rivets and nails are manufactured paint.
alan while powder is used in making Among defence materials, aluminium is king.
Text read from the printed page and cleaned; old type leaves the occasional error.